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Abstract:

An sealing gasket is shown for use in forming joints of plastic pipe. The
gasket is formed as a composite elastomeric body with a leading region
formed of a thermoplastic elastomer material and with a trailing region
formed of a synthetic plastic material. The gasket body has an outer
circumferential region provided with a series of recessed pocket which
give it a scallop-like appearance. The relatively harder plastic region
of the gasket body deforms the associated pipe socket end during
manufacture of the pipe end, whereby the gasket is integrally locked
within an internal pipe groove in the pipe socket end upon completion of
the pipe belling operation.

Claims:

1. A pipe sealing gasket designed for receipt within a groove provided
within a socket end of a thermoplastic pipe for sealing engagement and
forming a pipe joint with a mating male pipe having an exterior pipe
surface, the gasket comprising:a ring shaped composite elastomeric body
which, when viewed in cross section, has a leading region formed of a
thermoplastic elastomer material and which has a trailing region formed
of a synthetic plastic material, the leading region having an outer
surface and an inner primary sealing surface which forms a seal with the
exterior surface of the mating male pipe when the mating male pipe is
inserted within the socket end of the thermoplastic pipe to form a pipe
joint; andwherein the trailing body region of the gasket has a series of
recessed pockets formed therein which provide a scallop-like pattern on
the outer surface of the trailing region of the gasket body, the recessed
pockets being located at evenly spaced locations about an outer
circumferential region of the gasket body, and wherein the outer
circumferential region of the gasket body contacts the groove provided
within the socket end of a thermoplastic pipe during pipe belling
operations as the socket end is heated to thereby deform the socket end
and integrally lock the gasket body within the socket end during the
belling operation.

2. The gasket of claim 1, wherein the contact between the gasket body and
the socket end of the thermoplastic pipe during the belling operation
structurally integrates the gasket body with the pipe socket end so that
the trailing region of the gasket body is no longer required to act as a
discrete structural member in the resulting pipe joint.

3. The gasket of claim 1, wherein the thermoplastic elastomer material is
selected from the group consisting of TPE's and TPV's.

4. The gasket of claim 1, wherein the synthetic plastic material is a
polyolefin material.

5. The gasket of claim 1, wherein the leading region of the ring shaped
composite elastomeric body has an outer surface and an inner primary
compression sealing surface which forms a compression seal with the
exterior surface of the mating male pipe when the mating male pipe is
inserted within the socket end of the thermoplastic pipe to form a pipe
joint.

6. A method of forming a pipe joint using a pipe sealing gasket designed
for receipt within a groove provided within a female socket end of a
first section of pipe for forming a seal between an internal surface of
the female socket end and a male spigot end of a mating second pipe
section, the method comprising the steps of:installing a sealing gasket
within the groove provided within the female socket end of the first pipe
section, the sealing gasket being formed as a ring shaped composite
elastomeric body which, when viewed in cross section, has a leading
region formed of a thermoplastic elastomer material and which has a
trailing region formed of a synthetic plastic material, the leading
region having an outer surface and an inner primary compression sealing
surface which forms a compression seal with the exterior surface of the
mating male pipe when the mating male pipe is inserted within the socket
end of the thermoplastic pipe to form a pipe joint;wherein the trailing
body region of the gasket has a series of recessed pockets formed therein
which provide a scallop-like pattern on the outer surface of the trailing
region of the gasket body, and wherein the outer circumferential region
of the gasket body contacts the groove provided within the socket end of
a thermoplastic pipe during pipe belling operations as the socket end is
heated to thereby deform the socket end and integrally lock the gasket
body within the socket end during the belling operation, wherein the
contact between the gasket body and the socket end of the thermoplastic
pipe during the belling operation structurally integrates the gasket body
with the pipe socket end so that the trailing region of the gasket body
is no longer required to act as a discrete structural member in the
resulting pipe joint;installing the spigot end of one thermoplastic pipe
section within the socket end of a second pipe section to form a pipe
joint.

7. The method of claim 6, wherein the thermoplastic elastomer material is
selected from the group consisting of TPE's and TPV's.

8. The method of claim 7, wherein the synthetic plastic material is a
polyolefin material.

9. A method of installing a gasket in a socket end of a thermoplastic pipe
which is used to form a pipe joint, the method comprising the steps
of:providing a mandrel with an inner end and an outer end and having an
outer working surface;installing a gasket at a first circumferential
position on the outer working surface;heating a socket end of the
thermoplastic pipe; forcing the heated socket end of the thermoplastic
pipe over the working surface of the mandrel and over the gasket and
backup collar, whereby the heated socket end of the thermoplastic pipe
flows over the gasket to form a retention groove for retaining the
gasket;cooling the heated socket end of the thermoplastic pipe;retracting
the cooled socket end of the thermoplastic pipe and the retained gasket
from the working surface of the mandrel;the sealing gasket being formed
as a ring shaped composite elastomeric body which, when viewed in cross
section, has a leading region formed of a thermoplastic elastomer
material and which has a trailing region formed of a synthetic plastic
material, the leading region having an outer surface and an inner primary
compression sealing surface which forms a compression seal with the
exterior surface of the mating male pipe when the mating male pipe is
inserted within the socket end of the thermoplastic pipe to form a pipe
joint;wherein the first circumferential region provided on the working
surface of the mandrel comprises a circumferential groove having opposing
sidewalls, and wherein the gasket body is seated within the
circumferential groove so that the thermoplastic pipe is forced over the
trailing region of the gasket body and then over the leading region
thereof, contact with the trailing region of the gasket body acting to
deform the bell pipe end and integrally lock the gasket body within the
subsequently formed retention groove in the pipe socket end.

10. The method of claim 9, further comprising the steps of:providing a
backup collar at a second circumferential location on the mandrel, the
backup collar having an exposed lip portion which initially abuts the
gasket;wherein the backup collar is retracted once the heated
thermoplastic pipe end is forced over the forming mandrel and the gasket.

11. The method of claim 10, further comprising the step of applying a
vacuum or positive external pressure to the heated, socket end of the
thermoplastic pipe after the pipe has been forced over the working
surface of the gasket and mandrel to thereby force the heated, socket end
to contract about the mandrel and gasket.

12. The method of claim 11, wherein the heated thermoplastic pipe is
cooled by water or air after the mandrel is retracted.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The present invention relates generally to sealing systems for
thermoplastic pipes and, more specifically, to an improved pipe gasket
and to an improved belling process for installing a gasket in a socket
end of a thermoplastic pipe.

[0003]2. Description of the Prior Art

[0004]Pipes formed from thermoplastic materials including polyethylene and
PVC are used in a variety of industries. In forming a joint between
sections of pipe, the spigot or male pipe end is inserted within the
female or socket pipe end. An annular, elastomeric ring or gasket is
typically seated within a groove formed in the socket end of the
thermoplastic pipe. As the spigot is inserted within the socket, the
gasket provides the major seal capacity for the joint. It is critical,
during the installation process, that the gasket not be able to twist,
flip or be displaced, since a displaced or dislocated gasket will
adversely affect the ultimate sealing capacity of the joint.

[0005]In the early 1970's, a new technology was developed by Rieber & Son
of Bergen, Norway, referred to in the industry as the "Rieber Joint." The
Rieber system employed a combined mold element and sealing ring for
sealing a joint between the socket end and spigot end of two cooperating
pipes formed from thermoplastic materials. In the Rieber process, the
elastomeric gasket was inserted within an internal groove in the socket
end of the female pipe as the female or belling end was simultaneously
being formed. The provision of a prestressed and anchored elastomeric
gasket during the belling process at the pipe factory provided an
improved socket end for a pipe joint with a sealing gasket which would
not twist or flip or otherwise allow impurities to enter the sealing
zones of the joint. These features increased the reliability of the joint
and decreased the risk of leaks or possible failure due to abrasion or
other factors. The Rieber process is described in the following issued
U.S. Pat. Nos. 4,120,521; 4,061,459; 4,030,872; 3,965,715; 3,929,958;
3,887,992; 3,884,612; and 3,776,682.

[0006]In the Rieber process, the gasket is installed in a circumferential
groove provided upon the working surface of a mandrel and abuts a backup
collar which helps to position and retain the gasket during the
subsequent belling operation. The associated thermoplastic pipe was then
heated and the heated thermoplastic pipe end was forced over the mandrel
and gasket. The pipe socket end was deformed by the gasket and an
internal retention groove was formed in the interior of the pipe end. The
pipe end was then cooled so that it would retain its shape and the
mandrel was retracted, leaving the sealing gasket fixed within the
retention groove.

[0007]In the Rieber process, the gasket always included an internal metal
reinforcing component which circumscribed the gasket body and gave it
additional rigidity. The metal component, either a band or wire, was
bonded to the rubber and acted as the structural member to keep the
gasket engaged in the pipe socket after the belling operation was
complete. As such, although the pipe wall was formed over the Rieber
gasket, the two components were discrete.

[0008]Other commercial gaskets available in the industry, for example the
Forsheda POWER LOCK® and the Vassallo EPSMI®, did not utilize a
bonded metal component, but instead used a hard polymer component for the
trailing region (ramp). The hard polymer component acted in the same
structural manner as the metal component in the original Rieber belling
operation. As such, the hard polymer portion of the gasket was
necessarily heavy with a relatively thick cross section. The pipe wall
was formed over the gasket and these two components again remained
discrete in the final assembly. In those cases where material was removed
from the trailing region of the gasket, as in the Vassallo gasket, it was
removed to reduce mass while retaining structural integrity.

[0009]A need exists, therefore, for an improved sealing gasket for use in
a Rieber type manufacturing process, which sealing gasket would be even
more positively and "integrally locked" within the retention groove of
the socket pipe end during the belling operation.

[0010]A need also exists for such a sealing gasket which would be simple
in design and simple to manufacture and which could also be used without
the necessity of modifying the design of existing belling machines.

[0011]A need also exists for such a sealing gasket which, because of its
composite construction, would eliminate the need for an internal
reinforcing ring, thereby reducing the cost of the gasket and simplifying
the belling operation and improving the cycle time of the manufacturing
operation.

[0012]A need also exists for such a sealing gasket which, due to its
composition, would eliminate the need for the use of a lubricant during
the belling operation.

[0013]A need also exists for such a gasket which could be color coded so
that, for example, the gasket could be coded according to size or end
use.

[0014]A need also exists for such a gasket which, due to its composition,
could utilize recycled scrap, thereby eliminating much of the scrap waste
present in conventional belling operations.

SUMMARY OF THE INVENTION

[0015]The present invention has as its object to provide an improved
sealing gasket, an improved pipe belling process, and an improved pipe
assembly method, all of which meet the needs described in the prior art
and which meet the previous objectives. The belling process and pipe
joint of the invention uses a special "scallop" design in a hard polymer
region of the gasket body to integrate the gasket and the pipe wall. As
compared to the previously described Rieber and Forsheda processes, the
pipe wall and the trailing region (ramp) interface of the gasket body is
no longer two smooth mating surfaces. Now the pipe wall is formed over
the gasket at a temperature above its glass transition temperature. Then,
either using vacuum or pressure, the pipe wall is forced to flow into
cavities formed by the scalloped regions of the gasket. Now integrated
with the pipe wall, the hard polymer component of the subject gasket is
no longer required to act as the discrete structural member seen in the
previous gasket designs described in the prior art. The structural
integration apparent in the new design provides for optimal design of the
trailing region of the gasket body.

[0016]The improved pipe sealing gasket of the invention is designed for
receipt within a groove provided within a socket end of a thermoplastic
pipe. The gasket has a ring shaped composite elastomeric body which, when
viewed in cross section, has a leading region formed of a thermoplastic
elastomer material (TPE) and which has a trailing region formed of a
synthetic plastic material. The leading region has an outer surface and
an inner primary compression sealing surface which forms a compression
seal with the exterior surface of the mating male pipe when the mating
male pipe is inserted within the socket end of the thermoplastic pipe to
form a pipe joint. The trailing body region of the gasket has a series of
recessed pockets formed on an outer surface thereof which provide a
scallop-like pattern on the outer surface of the trailing region of the
gasket body.

[0017]Preferably, the thermoplastic elastomer material is selected from
the group consisting of thermoplastic elastomers (TPE's) and
thermoplastic vulcanizable elastomers (TPV's). The preferred material for
the synthetic plastic material is preferably a polyolefin material, such
as polypropylene. The recessed pockets which provide the scallop-like
pattern on the outer surface of the trailing region of the gasket body
are preferably located at evenly spaced locations about an outer
circumferential region of the gasket body. The resulting outer
circumferential region of the gasket body contacts and deforms the groove
provided within the socket end of a thermoplastic pipe during pipe
belling operations as the heated pipe end is flowed, to thereby
integrally lock the gasket body within the pipe bell during the belling
operation.

[0018]In the method of forming a pipe joint of the invention, a sealing
gasket of the type previously described is pre-located within a groove
provided within a female socket end of a first section of pipe in a
Rieber style manufacturing process. The spigot end of one section of
thermoplastic pipe is then inserted within the socket end of a second
pipe section to form a pipe joint. The socket end of the thermoplastic
pipe terminates in a mouth region with the groove being located adjacent
the mouth region. Upon assembly of the joint, the primary compression
seal region of the gasket body forms a compression seal with the mating
spigot pipe end.

[0019]In the improved pipe belling method of the invention, a forming
mandrel is provided with an inner end and an outer end, the mandrel also
having an outer working surface. An improved gasket of the type
previously described is installed at a first circumferential position on
the outer working surface of the mandrel. The first circumferential
region preferably comprises a circumferential groove having opposing
sidewalls, and wherein the gasket body is seated within the
circumferential groove so that the thermoplastic pipe is forced over the
trailing region of the gasket body and then over the leading region
thereof. Heating the thermoplastic pipe end above the glass transition
temperature allows the resulting rubbery polymer to flow about the gasket
body, including the scalloped regions. This action of the heated socket
end of the thermoplastic pipe flowing over the gasket also forms the
retention groove which ultimately retains the sealing gasket. The heated
socket end of the thermoplastic pipe is then cooled and the socket end is
retracted from the mandrel, whereby the gasket is retained within an
internal groove which is formed in the interior of the female, belled
pipe end. The unique composition and geometry of the gasket of the
invention insures that the gasket body is integrally locked into position
within the retention groove provided in the socket pipe end.

[0020]Additional objects, features and advantages will be apparent in the
written description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a perspective view of the socket end of a section of
thermoplastic pipe, partly broken away, and showing the sealing gasket of
the invention in cross-section and installed within the internal
retention groove of the pipe.

[0022]FIG. 2 is a perspective view of the sealing gasket of the invention
showing the scallop-like external circumferential region thereof.

[0023]FIG. 3 is a cross-sectional view of the gasket of the invention
showing the relative leading and trailing body regions thereof.

[0024]FIGS. 4-7 illustrate the prior art Rieber pipe forming process with
the pipe gasket of the invention in place on the outer working surface of
the belling mandrel.

DETAILED DESCRIPTION OF THE INVENTION

[0025]The embodiments herein and the various features and advantageous
details thereof are explained more fully with reference to the
non-limiting embodiments that are illustrated in the accompanying
drawings and detailed in the following description. Descriptions of
well-known components and processes and manufacturing techniques are
omitted so as to not unnecessarily obscure the embodiments herein. The
examples used herein are intended merely to facilitate an understanding
of ways in which the invention herein may be practiced and to further
enable those of skill in the art to practice the embodiments herein.
Accordingly, the examples should not be construed as limiting the scope
of the claimed invention.

[0026]The primary advantages of the present invention can perhaps be best
understood with reference to a simplified discussion of the prior art
Rieber pipe belling process and with reference first to FIGS. 4-7 of the
drawings. FIG. 4 shows a section of the improved composite elastomeric
sealing gasket of the invention 11 in place on the generally cylindrical
outer working surface 15 of the mandrel 17 used in the belling process.
It should be noted that, because of the composite nature of the improved
gasket of the invention, there is no need for a metal reinforcing ring to
be embedded in the gasket body. The exact make-up of the composite
elastomeric gasket 11 will be further described below. As can be seen
from FIG. 2, the gasket is a ring shaped, circumferential member having
an inner compression surface (19 in FIGS. 3-4) and an exposed nose
portion 21 which, as shown in FIG. 4, abuts a backup or forming collar
23. The nose portion 21 forms a contact area for contacting the lip
portion 22 of the backup collar 23. The backup collar 23 FIG. 4) has a
first generally cylindrical extent 25 which is joined to a second
cylindrical extent 27 by a step region 29, whereby the second extent 27
is of greater external diameter than the first cylindrical extent 25. The
lip portion 22 of the backup collar 23 forms a right angle with respect
to the working surface 15 of the mandrel 17.

[0027]In the first step of the Rieber pipe belling process, the composite
gasket 11 is placed onto the working surface of the mandrel 17 and pushed
to a position against the back-up or forming collar 23. In this position,
the gasket is anchored to the mandrel surface.

[0028]In the second step of the manufacturing process, the socket end 33
of the thermoplastic pipe 31 (FIG. 5) is heated and pushed over the steel
mandrel 17, gasket 11 and back-up collar 23. The socket end 33 is
expanded due to the thermoplastic nature of the pipe. A number of
thermoplastic materials, such as polyethylene, polypropylene and
polyvinylchloride (PVC) are known in the prior art having the required
expansion characteristics, depending upon the end application of the pipe
joint. The preferred material for the pipe is PVC. The socket end 33 of
the PVC pipe flows over the first cylindrical extent 25 of the back-up
collar 23 and abuts the step region 29 in the second step of the process.

[0029]In the next step of the pipe belling process (FIG. 6) the mandrel
and pipe move away from the back-up collar 23 and the pipe socket end 33
retracts around the mandrel and gasket 11 due to the elastic forces of
the thermoplastic material. Typically, a vacuum is also applied through
ports 35, 37 which connected the mandrel working surface with a vacuum
source (not shown).

[0030]In the final step of the process (FIG. 7), the pipe socket end 33 is
cooled by means of a water spray bar 39 and spray nozzles 41. As the
cooling takes place, the pipe socket end 33 shrinks around the gasket 11.

[0031]The above described Rieber process has been in commercial use since
the early 1970's and is described in the above referenced issued United
States patents, among other sources. It will thus be well familiar to
those skilled in the thermoplastic pipe sealing arts. However, it is the
particular geometry and composition of the improved sealing gasket 11 of
the invention which results in an improved pipe product. These features
of the gasket 11 will now be described in greater detail.

[0032]FIG. 1 of the drawings shows the pipe sealing gasket of the
invention, which is designated generally as 11, the gasket being received
within a groove (43 in FIG. 1) provided within a socket end 45 of a
thermoplastic pipe. The pipe socket end (45 in FIG. 1) has been formed
about the gasket 11 of the invention using the previously described
Rieber process. As will be appreciated from FIGS. 1 and 3, the sealing
gasket 11 of the invention has a ring shaped composite elastomeric body
which, when viewed in cross section (FIG. 3), has a leading region 47
formed of a "thermoplastic elastomer material" or (TPE), and which has a
trailing region 49 formed of a "synthetic plastic material."

[0033]As can be seen in FIG. 3, the leading region 47 of the gasket body
has an outer surface 51 which continues around the nose portion 21 to
form an inner surface 53 which slopes downwardly as viewed in FIG. 3 to
form a primary compression sealing surface (shown generally as 19) of the
gasket. The compression sealing surface 19 forms a compression seal with
the exterior surface of the mating male pipe (not shown) when the mating
male pipe is inserted within the socket end (45 in FIG. 1) of the
thermoplastic pipe to form a pipe joint. The mating male pipe is
typically formed of the same PVC material as the female pipe end and is a
plain cylindrical member. It should be noted that, to the best of
Applicant's knowledge, none of the presently existing composite sealing
gasket designs used in the industry incorporate a compression sealing
region. Rather, the standard designs in the industry at the present time
use a lip seal as the primary sealing surface of the gasket body.

[0034]With further reference to FIG. 3, the compression sealing region of
the gasket body slopes upwardly at lower surface 55, eventually forming a
flattened tail region 57. The region illustrated generally at 57 in FIG.
3 may constitute a secondary sealing region of the gasket. The trailing
tip 58 of the gasket body defines a sharp, angular region of the gasket
body between the flattened tail region 57 and an outer surface 59. The
outer surface 59 of the tail region 57 makes up the trailing body region
of the gasket and has a series of recessed pockets 61 formed therein
which provide a scallop-like pattern (best seen in FIG. 2) on the outer
surface 59 of the trailing region of the gasket body. By scallop-like is
meant, i.e., one of a continuous series of circle segments or angular
projections forming a border (as on cloth or metal), Merriam-Webster's
Online Dictionary, 2008.

[0035]As best seen in FIGS. 2 and 3, the scallops form recessed regions
(61 in FIG. 3) which are generally triangular in cross section having a
horizontal lower extent 62 joined to a vertical extent 64, as viewed in
FIG. 3. In the embodiment illustrated, the horizontal lower extents 62
form a long leg of the triangular cross section, while the vertical
extents 64 form a short leg. In the example illustrated, the long legs 62
are approximately twice the length of the short legs 64. The recessed
regions 61 which provide the scallop-like pattern on the outer surface 59
of the trailing region 49 of the gasket body are preferably located at
evenly spaced locations about an outer circumferential region (63 in FIG.
2) of the gasket body with the lower extents 62 thereof being generally
parallel and with the vertical extents 64 extending radially outward from
the diametral axis 66 of the gasket.

[0036]As has been briefly explained, the outer circumferential region 61
of the gasket body contacts the groove (43 in FIG. 1) provided within the
socket end 45 of the thermoplastic pipe during pipe belling operations to
thereby integrally lock the gasket body within the pipe bell during the
belling operation. Because the trailing region of the gasket is formed of
a synthetic plastic material, the relatively harder nature of this region
actually deforms the pipe bell groove region, the deformed regions being
indicated as the striations 65 in FIG. 1 of the drawings. In other words,
as the socket end 45 of the thermoplastic pipe is heated above its glass
transition temperature, it becomes rubbery in nature and actually flows
about the scalloped recesses. Because the scallop-like regions of the
harder gasket body actually form a sort of indentation in the interior of
the mouth of the pipe socket end as the pipe end cools during
manufacture, the gasket is positively locked into position within the
pipe mouth.

[0037]The terms "thermoplastic elastomer material" and "synthetic plastic
material" are intended to be terms of art, as will be explained in
greater detail in the paragraphs which follow. The nature of the
materials used in forming the gasket body are significant due to that
fact that, unlike the standard prior art gasket formed totally of a
traditional elastomer, such as natural or synthetic rubber, the
"composite gasket" of the invention has a leading region of a relatively
softer (lower durometer) thermoplastic elastomer material (TPE) and a
trailing region of a relatively harder (higher durometer) synthetic
plastic material.

[0038]Turning first to the trailing region of the gasket body, the
relatively harder synthetic plastic material is preferably a polyolefin,
such as polypropylene, polypropylene, polyvinylchloride, etc. A preferred
material for the synthetic plastic region of the gasket is polypropylene.
The preferred polypropylene material is a high performance impact
copolymer showing an appropriate stiffness for the application at hand.
The material can be of higher durometer than the remaining portion of the
gasket body since it does not participate in the sealing function of the
gasket to any significant extent.

[0039]Turning now to the material used to form the leading region of the
gasket body, the term "thermoplastic elastomer material" (referred to
herein by the shorthand term "TPE") is a relatively newer family of
materials known in the industry, as will be explained with reference to
the previously used materials. The term "elastomer" as used herein will
be intended to mean "any of various polymers having the elastic
properties of natural rubber." Similarly, the term "plastic" will be used
herein to mean "any of various organic compounds produced by
polymerization, capable of being molded, extruded, cast into various
shapes and films, or drawn into filaments."

[0040]Applicant's use of the term "thermoplastic elastomer material" or
TPE is intended to encompass a special type of recently developed
"engineered" elastomer. The members of this subset include, for example:

[0041]The preferred thermoplastic elastomer material used for Applicant's
leading region is a TPE "vulcanizate." These materials are polypropylene
based elastomers that exhibit excellent compression set, flex fatigue and
low/high temperature performance. They show very good chemical resistance
quite appropriate for conveying the fluids found in sewer/waste water
systems. Unlike the traditional elastomers used in sealing gasket
manufacture, these products can be recycled and reprocessed since the
physical and chemical properties of the materials are not degraded. The
material can also be thermally bonded to form high strength bonds and in
the present application, both the TPV and the PP are perfectly bonded due
to their excellent compatibility.

[0042]An invention has been provided with several advantages. The improved
sealing gasket is simple in design and economical to manufacture. The
gasket features a "dual durometer" aspect in that the polypropylene
trailing region is more rigid than the remainder of the leading region of
the gasket body. The polypropylene planar, angled region of the gasket
replaces rubber at neutral locations for sealing purposes. The
polypropylene material provides the gasket with a very low coefficient of
friction between the gasket and the PVC material of the pipe socket end.
The polypropylene portion of the gasket has enough stiffness and rigidity
to retain the gasket in the proper position on the belling mandrel during
the belling process without deformation. The new shape enforces a more
stable bell shape during subsequent belling operations and improves
quality control. The new gasket is compatible with existing belling
machines. The improved sealing gasket can be used in a Rieber type
manufacturing process, but is more positively "integrally locked" within
the retention groove of the socket pipe end during the belling operation.
Because of the composite nature of the gasket body, the need for an
internal metal reinforcing band is eliminated, thereby simplifying the
belling operation and improving the cycle time of the manufacturing
operation. The plastic portion of the gasket prevents "pivoting" the
whole body of the gasket during belling, thus making the gasket more
tolerant of off-center assemblies on the forming mandrel. Possibilities
of "fish mounting" are minimized. The material make-up of the gasket body
also eliminates the need for a lubricant during the belling operation.
The materials of the gasket body make it suitable for color coding so
that, for example, the gasket could be coded according to size or end
use, e.g., as a sewer gasket or as a pressure gasket. Because of the
plastic-like nature of the materials used to form the gasket body, any
scrap material can be reused or recycled, thereby eliminating much of the
scrap waste present in conventional belling operations. The sealing
region of the gasket is formed of a suitable TPE material which allows
bonding to the polypropylene (plastic) region of the gasket.

[0043]The gasket of the invention provides an ideal solution for PVC pipe
joints. It can be used for applications in sewer, pressure and telephone
or optic duct, as well as with PVC pipe.

[0044]While the invention has been shown in only one of its forms, it is
not thus limited but is susceptible to various changes and modifications
without departing from the spirit thereof.